Adiponitrile (ADN) is a commercially important and versatile intermediate in the industrial production of nylon polyamides useful in forming films, fibers, and molded articles. ADN can be produced by hydrocyanation of 1,3-butadiene (BD) in the presence of transition metal complexes including various phosphorus-containing ligands. For example, catalysts including nickel and monodentate phosphorus-containing ligands are well documented in the prior art; see, for example, U.S. Pat. Nos. 3,496,215; 3,631,191; 3,655,723 and 3,766,237; and Tolman, C. A., McKinney, R. J., Seidel, W. C., Druliner, J. D., and Stevens, W. R., Advances in Catalysis, 1985, Vol. 33, pages 1-46. Improvements in the hydrocyanation of ethylenically unsaturated compounds with catalysts including nickel and certain multidentate phosphite ligands are also disclosed; e.g., see: U.S. Pat. Nos. 5,512,696; 5,821,378; 5,959,135; 5,981,772; 6,020,516; 6,127,567; and 6,812,352.
3-Pentenenitrile (3PN) can be formed through a series of reactions as illustrated below.

According to abbreviations used herein, BD is 1,3-butadiene, HC≡N is hydrogen cyanide, and 2M3BN is 2-methyl-3-butenenitrile. A method to increase the chemical yield of 3PN from BD hydrocyanation includes the catalytic isomerization of 2M3BN to 3PN (Equation 2 above) in the presence of NiL4 complexes as disclosed in U.S. Pat. No. 3,536,748. Co-products of BD hydrocyanation and 2M3BN isomerization can include 4-pentenenitrile (4PN), 2-pentenenitrile (2PN), 2-methyl-2-butenenitrile (2M2BN), and 2-methylglutaronitrile (MGN).
In the presence of transition metal complexes including various phosphorus-containing ligands, dinitriles such as ADN, MGN, and ethylsuccinonitrile (ESN) can be formed by the hydrocyanation of 3PN and 2M3BN, as illustrated in Equations 3 and 4 below. Equation 4 also shows that 2M2BN can be formed when 2M3BN undesirably isomerizes in the presence of a Lewis acid promoter that can be carried over from a pentenenitrile hydrocyanation reaction zone. Equation 5 shows that 2M2BN can be formed when 2M3BN undesirably isomerizes.

The hydrocyanation of activated olefins such as conjugated olefins (e.g., 1,3-butadiene) can proceed at useful rates without the use of a Lewis acid promoter. However, the hydrocyanation of un-activated olefins, such as 3PN, require at least one Lewis acid promoter to obtain industrially useful rates and yields for the production of linear nitriles, such as ADN. For example, U.S. Pat. Nos. 3,496,217, 4,874,884, and 5,688,986 disclose the use of Lewis acid promoters for the hydrocyanation of non-conjugated ethylenically unsaturated compounds with nickel catalysts including phosphorus-containing ligands.